One source said: “The girls are likely to suffer when they take to the stage – not just as a result of the aggression over Crimea but also because of Putin’s homophobia, which won’t please a crowd consisting largely of gay men.”

Speaking from Copenhagen, the source added: “The backlash is being treated as inevitable by the organisers. Attitudes towards Russia are at an all-time low and it doesn’t matter that the girls, Nastya and Masha, are cute as buttons – many other nations are going to let their feelings be known. The chance of them getting through are slim.”

But some experts are predicting that pro-Putin viewers across the former Soviet states including Azerbaijan, Armenia, Moldova and even Ukraine could vote en masse in a bid to try and influence the outcome.

The teenage sisters, from Kursk, won the chance to represent their country after beating competition from 200 other Russian acts. They previously won Junior Eurovision in 2006, at the tender age of nine.

The blonde pair will compete directly against Ukranian singer Mariya Yaremchuk, who is among the favourites to win. Both countries take the contest very seriously and neither has missed a place in the final since the current system began in 2004.

To complicate matters, Ukraine’s Mariya is privately a fan of Putin, who is suspected of plotting a full-scale invasion of Ukraine, with the military there currently on “full combat alert”.

Ukraine’s Mariya: Putin fan

A source close to the Ukranian delegation said: “Mariya is having to toe the party line in interview - saying how tough things are for the people of Ukraine right now – but she is actually very much pro-Putin. This is another headache for the organisers, because it could cause trouble if people realise she supports the Russians.”

Political issues and Eurovision have long gone hand in hand, with many nations voting for their allies and neighbours regardless of the quality of the song.

The semi-finals were introduced a decade ago in order to whittle out the weakest acts so that only the 26 best compete in the international show on the night. Ten acts go through from each of the semi-finals, while the ‘big five’ countries who finance the event – which includes the UK – get automatic entry along with the host nation.

The UK’s act, Molly Smitten-Downes, is considered to be one of our strongest for several years, following disastrous performances from Bonnie Tyler and Engelbert Humperdinck.

After impressing with her song, Children of the Universe, during rehearsals this weekend Molly was placed as third favourite to win with some bookies.

She is already the most heavily backed competitor since Jade Ewen sang an Andrew Lloyd-Webber number in 2009.